Synergistic mixture of zinc dialkyldithiophosphate and zinc dialkylphenoxyethyldithiophosphate

ABSTRACT

A synergistic mixture comprising zinc dialkyldithiophosphate and zinc dialkylphenoxyethyldithiophosphate, said mixture provides improved oxidation resistance, nitration inhibition and antiwear properties to a wide variety of organic oil substrates.

United States Patent 11 1 Brown et al. H IMarch 13, 1973 SYNERGISTIC MIXTURE OF ZINC [56] References Cited DIALKYLDITHIOPHOSPHATE AND ZINC DIALKYLPHENOXYETHYL- UNTED STATES PATENTS DITHIOPHOSPHATE 3,230,371? Z1972 Wiiey et aL] ..252/3 2.7 E 3. 2, 1966 W' t .252 32.7 1 Inventors: Thomas Bmwn, Nederland; 3,216,936 11/1965 Le ..2s2i32.7

James H. Cupit, Port Arthur, both of Primary Examiner-Daniel E. Wyman Assistant Examiner-4. Vau hn '13 A :T I .N Yk,N.Y. g 1 Sslgnee exam nc ew or Attorney-Thomas H. Whaley and Carl G. Ries [22] Filed: Dec. 9, 1970 211 Appl. No.: 96,396 [57] ABSTRACT A synergistic mixture comprising zinc dialkyldithiophosphate and zinc dialkyiphenoxyethyl- [52] U.S. Cl. ..252/32.7 E, 44/68, 4421251046 dithiophosphate, Said mixture provides improved idation resistance nitration inhibition and antiwear [5i] lnt.Cl. ..C10m l/48,Cl0m 3/42 t t f t [58] Field of Search ..252/32.7 E, 400 proper 0 a e vane y 0 organ: Subma 6 Claims, 1 Drawing Figure DIR (ABS 1cm) PATENTEDMAR 1 31913 E LOAD EAR INDEX [3 18 (ANTI-WEAR? 4| A '6 l2 a 5 .|4 AW 9 5 IO O 37 Z o J l n I I l l l 1 32 r I I 2 1 Q 3 I 2 .L l I 2' T E 3 4 s a a: WEIGHT RATIO ZADPzZPEP n. 'j (0.1% Zn) N a- 8. 3

INVENTORS THOMAS 0. BROWN JAMES H. CUPIT SYNERGISTIC MIXTURE OF ZINC DIALKYLDITHIOPHOSPHATE AND ZINC DIALKYLPIIENOXYETHYLDITHIOPHOSPIIATE BACKGROUND OF THE INVENTION Oil substrates are utilized in a wide variety of applications wherein, as a result of exposure to atmospheric conditions and/or elevated temperatures and/or severe operating conditions, thermal and oxidative degradation are frequently encountered. Such degradation is 1 usually manifested by deterioration in appearance, physical properties and performance on the part of the affected substrate. For example, the formation and deposition of so-called varnishes and sludge on engine surfaces is due primarily to oxidation and polymerization of lubricating oils. Such deposits are undesirable inasmuch as they contribute to wear and corrosion of engine surfaces.

The incorporation of a wide variety of additives has been proposed in an effort to find an effective means for stabilizing such substrates. In addition to providing effective stabilization, such additives must also possess other essential characteristics. Thus, they must be capable of being readily incorporated into the selected oil substrate; they must be compatible with such substrates; they must be able to provide extended stability thereto; and they must be able to maintain their own integrity under the conditions of use.

Among the prior art stabilizing additives are included metallo-organic compounds such as phosphate, phenolates, and sulfonates, as well as other organic compounds containing sulfur, phosphorus, and/or nitrogen such as organic amines, sulfides, hydroxy sulfides and phenols. Metals such as zinc, barium, and calcium are normally used when metals are incorporated into the aforementioned stabilizing additives. In addition, heavy metal salts of esters of dithiophosphoric acid and heavy metal salts of esters of phenoxyethyldithiophosphoric acid have been used as antioxidants and antiwear agents in crankcase and gear oils. However, few, if any, of the prior art stabilizing additives have provided the total effectiveness desired of them.

SUMMARY OF THE INVENTION It is the primary object of this invention to prepare stabilizing systems for oil substrates which exhibit a high degree of prolonged total stabilizing effectiveness.

Various other objects and advantages of this invention will become apparent from the following description thereof.

We have now surprisingly discovered that by combining a zinc dialkyldithiophosphate with a zinc dialkylphenoxyethyldithiophosphate in a weight ratio of from about 4:1 to 1:4, and preferably in a weight ratio of 3:1, all of the previously described requirements for a stabilizing system are met. Thus, this system is effective in a wide variety of oil substrates, is compatible with such substrates, is able to provide prolonged stability and is able to provide total effectiveness as regards improved oxidation resistance, nitration resistance and antiwear properties. of most significance, the novel blends of this invention exhibit outstanding synergistic stabilizing performance, i.e., the performance of the combination substantially exceeds the sum total of the performances exhibited by the individual components thereof.

This invention will be better understood from the following detailed description thereof together with the accompanying drawing which provides a graphic illustration of the synergistic properties of the novel blends of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Methods for preparing zinc dialkyldithiophosphates are well known to those skilled in the art. The basic method for preparing such materials involves reacting an alkyl compound with phosphorus pentasulfide and thereafter neutralizing the resulting alkyldithiophosphoric acid with a basic zinc salt, such as zinc oxide or zinc hydroxide, at temperatures not exceeding about F. and at atmospheric pressure, i.e.,

Certain variations in this basic procedure have been proposed. Thus, U.S. Pat. No. 2,466,408 discloses a process which is conducted in a mineral oil solution or dispersion; U.S. Pat. No. 2,480,673 discloses the reaction of the dialkyl dithiophosphoric acid with finely divided zinc; and U.S. Pat. No. 2,342,431 discloses the use of certain alkylated phenols in the preparation of the acid product.

A vastly improved process for preparing dialkyldithiosphosphates is disclosed in copending application Ser. No. 89,011; filed Nov. 12, 1970, and assigned to the assignee of the subject invention. This improved process involves reacting, in a closed pressure system, a dialkyl dithiophosphoric acid and a basic zinc salt in a heptane slurry at a temperature ranging between 180 -300 F. and under autogenous pressure conditions. The introduction of high temperatures and pressures into the reaction process results in the preparation of zinc dialkyldithiophosphates which exhibit improved stability characteristics.

For purposes of convenience and brevity in this specification, the zinc dialkyldithiophosphate will be referred to by the designation ZADP."

Methods for preparing zinc dialkylphenoxyethyldithiophosphate are also well known to those skilled in the art. A typical procedure for preparing these materials involves the reaction of p-alkyl substituted phenoxyethyl alcohol with phosphorus pentasulfide followed by the neutralization of the acid formed with a basic zinc salt, such as zinc carbonate or zinc oxide, i.e.

For purposes of brevity and convenience in this specification, the zinc dialkylphenoxyethyldithiophosphate will be referred to by the designation ZPEP.

As previously noted, these synergistic combinations are useful in any natural and synthetic, hydrocarbon and substituted hydrocarbon oil substrate wherein oxidative or thermal degradation is a problem. Among such oil substrates are included: lubricating oils such as those of the aliphatic ester type, e.g., dihexyl azelate, di-(2-ethylhexyl)azelate, di-(3,5,5-trimethylhexyl)glutarate, di-(3,5,S-trimethylpentyl)-glutarate, di-(2- ethylhexyl)pimelate, di-(2-ethylhexyl)-adipate, diisoamyl adipate, triamyl tricarballate, pentaerythritol tetracaproate, dipropylene glycol dipelargonate, 1,5- pentanediol di-(2-ethylhexanoate), and the like; oils of animal and vegetable origin, e.g., linseed oil, menhaden oil, cod liver oil, castor oil, and the like; saturated and unsaturated hydrocarbons such as for example, both natural and synthetic gasolines, jet fuels, diesel oils, mineral oils, fuel oils, drying oils, and greases.

The blends of this invention can be intimately mixed with the oil substrate by any suitable means and at any stage prior to the utilization of the oil. The two components may be added to the selected substrate either individually or as a combined system. The treated substrate may be immediately utilized in its intended application or it may be satisfactorily stored for extended periods of time and thereafter utilized in the desired application.

With regard to the relationship between the concentration of the respective components, weight ratios of ZADPzZPEP ranging from about 4:1 to 1:4 are effective with maximum oxidation resistance, nitration inhibition and antiwear properties being obtained when a 3:1 weight ratio of ZADP:ZPEP is utilized. Furthermore, in order to provide this substantially improved stability to the various substrates, it is sufficient to utilize each component in the blend in a concentration which provides at least 0.1 percent zinc, based on the weight of the substrate. Needless to say, higher concentrations of zinc may be provided by each component, although the use of individual zinc concentrations exceeding about 0.20 percent, by weight, is unnecessary since such a practice does not provide the proportionate increases in stability which would warrant the cost involved in employing the stabilizers at such high concentration levels.

It should also be noted that the novel synergistic blends of this invention may be satisfactorily incorporated into oil substrates in conjunction with typical oil additives such, for example, as dispersants, detergents, other anti-oxidants, other antiwear agents, pour point depressants, anti-foamants, and the like.

The following examples will further illustrate the embodiment of this invention.

EXAMPLE I This example illustrates the outstanding synergistic stabilizing performance'resulting from the use of the novel blends of this invention.

The ZADP component utilized in this example was the zinc salt resulting from the reaction of a mixture of methylisobutyl carbinol and isopropanol with phosphorus pentasulfide in about a 2.7:2.3:l.0 mole ratio and then neutralizing the resulting dithiophosphoric acid with zinc oxide.

The ZPEP component utilized was the zinc salt of dinonylphenoxyethyldithiophosphate which was prepared by reacting p-nonyl phenoxyethyl alcohol with phosphorus pentasulfide and then neutralizing the resulting acid with zinc carbonate.

The value of the additive combinations was tested by adding the individual ZADP and ZPEP components, in varying weight ratios so as to provide 0.1 percent zinc, by weight, to a paraffinic base oil which also contained 6 percent, by weight, of an alkenylsuccinimide dispersant. The various test blends were formulated at F. with mechanical agitation for 30 minutes. Each of the resulting oil blends was then submitted to the following stability test procedures: Nitro-Oxidation Test This test was utilized to measure oxidation and nitration stability. The test consisted of bubbling an air-N0 gas mixture [-0.2 percent (V)NO through a cc oil sample for a period of 4.5 hours at a gas flow rate of 68 cc/min. and an oil temperature of 280 F. Differential infrared analysis was then run on the used oil sample with the degree of oxidation and nitration being determined by measuring the peaks at 5.85 and 6.14 microns, respectively. Load Wear Index This test is widely used for measuring wear preventive and extreme pressure qualities of lubricants under boundary conditions. The test is described in detail in Federal Test Method Standard No. 791, Method No. 6503.], issued July 27, 1964. In general, this test involves pressing a rotating steel ball against a triangle of three stationary steel balls lubricated with the test oil. A series of tests is made with various pressures on the rotating steel balls. When welding occurs, indicating failure of the lubricant, the scars on the stationary balls are measured and the load, in pounds per square inch, needed for breakdown of the lubricant film is calculated based on the applied pressure and the size of the scars.

The test results for the various oil samples were then plotted, the resulting graph being depicted in the drawing. The units of the nitro-oxidation test are indicated on the left axis of the graph,'the units of the Load Wear Index are noted on the right axis of the graph, and the ZADPzZPEP ratio is noted on the horizontal axis. Inspection of the graph clearly reveals that maximum improvement in oxidation and nitration stabilities as well as antiwear properties is achieved as the weight ratio of ZADPzZPEP approaches 3: l

Furthermore, the synergistic properties of the blend are also to be noted in the drawing. Thus, the stability values plotted for the sole use of ZADP and ZPEP do not approach those of the 3:1 blend nor does the sum total of the performances attained by the use of the individual components approach that of the 3:1 blend.

EXAMPLE II The improved stability of the novel blends of this invention was further illustrated by submitting the blends to a Climax Model V-l25 4-cycle natural gas engine field test. Thus, the respective additives were admixed with a paraffinic base oil at a temperature of 130 F. with stirring for a period of 30 minutes. The resulting oil sample was then run in the engine for a period of one month. Used crankcase oil samples were withdrawn at seven day intervals and at the end of the test. The samples were then tested for the rate of viscosity increase, the rate of oxidation as determined by measuring the neutralization number of the sample,

and the rate of oxidation and nitration as measured by the NitrogOxidation Test described in Example I. The results of these determinations are presented in the following table:

The results summarized above clearly indicate that the synergistic mixture of this invention exhibits improved resistance to oxidation and nitration.

Summarizing, this invention is seen to provide a novel class of synergistic stabilizing systems which imparts excellent oxidative and thermal stability to a wide variety of oil substrates.

Variations may be made in procedures, proportions and materials without departing from the scope of this invention as defined by the following claims.

What is claimed is:

1. A synergistic antioxidant composition comprising a mixture of a zinc dialkyldithiophosphate and a zinc dialkylphenoxyethyldithiophosphate, said components being present in the mixture in a weight ratio ranging from about 4:1 to 1:4.

2. The synergistic composition of claim 1, wherein said zinc dialkyldithiophosphate and said zinc dialkylphenoxyethyldithiophosphate are present in a 3:1 weight ratio.

3. A composition comprising a blend of: (l) a major amount of an organic oil substrate which is subject to oxidative'and thermal degradation; and (2) a minor amount of a synergistic antioxidant composition comprising a mixture of a zinc dialkyldithiophosphate and a zinc dialkylphenoxyethyldithiophosphate, said components being present in the mixture in a weight ratio ranging from about 4:1 to 1:4.

4. The blend of claim 3, wherein said zinc dialkyldithiophosphate and said zinc dialkylphenoxyethyldithiophosphate are present in said synergistic composition in a 3:1 weight ratio.

5. The blend of claim 3, wherein said synergistic composition contains at least 0.1 percent zinc, based on the total weight of said oil substrate.

6. The blend of claim 3, wherein said oil substrate is a lubricating oil. 

1. A synergistic antioxidant composition comprising a mixture of a zinc dialkyldithiophosphate and a zinc dialkylphenoxyethyldithiophosphate, said components being present in the mixture in a weight ratio ranging from about 4:1 to 1:4.
 2. The synergistic composition of claim 1, wherein said zinc dialkyldithiophosphate and said zinc dialkylphenoxyethyldithiophosphate are present in a 3:1 weight ratio.
 3. A composition comprising a blend of: (1) a major amount of an organic oil substrate which is subject to oxidative and thermal degradation; and (2) a minor amount of a synergistic antioxidant composition comprising a mixture of a zinc dialkyldithiophosphate and a zinc dialkylphenoxyethyldithiophosphate, said components being present in the mixture in a wEight ratio ranging from about 4:1 to 1:4.
 4. The blend of claim 3, wherein said zinc dialkyldithiophosphate and said zinc dialkylphenoxyethyldithiophosphate are present in said synergistic composition in a 3:1 weight ratio.
 5. The blend of claim 3, wherein said synergistic composition contains at least 0.1 percent zinc, based on the total weight of said oil substrate. 